Biochemical oxygen demand system

ABSTRACT

In a biochemical oxygen demand system for continuous determination of oxygen uptake of a large inhomogeneous biological sample, a respirometer continuously replaces oxygen used in the sample by a monometrically triggered electrolysis reaction. The electrolysis cell wherein the reaction takes place includes a monometer controlled switch and an oxygen generator with activating electrodes. As oxygen is chemically or biologically removed from the sample, it is replenished from the air space above the sample. Any oxygen and CO2 removed from the air space above the sample causes a slight vacuum, thereby activating the monometer controlled switch. This switch actuates a constant current source coupled to the oxygen generator electrodes and oxygen is replenished by electrolysis of a dilute acid solution. A measure of the amount of oxygen replaced is made by actuating a time pulse generator from the monometer controlled switch to produce pulses of constant width at fixed time intervals. These constant width pulses are applied to an impulse counter wherein a measure of the oxygen generated is made in accordance with Faraday&#39;&#39;s law on electrochemistry.

[ Nov. 13, 1973 BIOCHEMICAL OXYGEN DEMAND SYSTEM Inventors: David L. Pippen, Las Cruces, N.

Mex.; Gary R. Kramer, College Station, Tex.

[73] Assignee: Oceanography International Corporation, College Station, Tex.

Filed: Dec. 3, 1971 Appl. No.: 204,675

204/229, 195 B, l T

[56] References Cited UNITED STATES PATENTS 6/1972 Young 204/195 B 11/1966 Poepel et a1. 204/195 R 10/1971 Haas 204/230 2/1970 MacArthur 204/1 T Primary Examiner-John H. Mack Assistant ExaminerD. R. Valentine Attorney-D. Carl Richards et a1.

[57] ABSTRACT In a biochemical oxygen demand system for continuous determination of oxygen uptake of a large inhomogeneous biological sample, a respirometer continuously replaces oxygen used in the sample by a monometrically triggered electrolysis reaction. The electrolysis cell wherein the reaction takes place includes a monometer controlled switch and an oxygen generator with activating electrodes. As oxygen is chemically or biologically removed from the sample, it is replenished from the air space above the sample. Any oxygen and CO removed from the air space above the sample causes a slight vacuum, thereby activating the monometer controlled switch. This switch actuates a constant current source coupled to the oxygen generator electrodes and oxygen is replenished by electrolysis of a dilute acid solution. A measure of the amount of oxygen replaced is made by actuating a time pulse generator from the monometer controlled switch to produce pulses of constant width at fixed time intervals. These constant width pulses are applied to an impulse counter wherein a measure of the oxygen generated is made in accordance with Faradays law on electrochemistry.

6 Claims, 6 Drawing Figures CONSTANT POWER CURRENT,D.C. 38 SUPPLY i GENERATOR 4o ELECTROLYTlC MANOMETRIC OXYGEN 30 GENERATOR I SWITCH F 2 42 I- T T T "'1 W 1 I2 CONVERTER- WELL-MIXED BIOLOGICAL CO2 ALKALI ACCUMULATOR REACTOR, WASTES 7 C02 20 (DISPLAY) I MICROORGANISMS R R I TEMPERATURE INCUBATOR I4 SENSOR I J I 44 T KID 7 AUTOMATIC EMPERATURE I6 COOLING PRINTOUT CONDITIONER UNIT T I8 T TEMPERATURE J CONTROLLER Patented Nov .13, 1973 I 3,772,176

4 Shegts-Sheet 4 T (0) W 1 TIMER IN SIGNAL 7 COMMON (c) REF-DC COMMON I I =/l A /l 0c REF I I I COMMON I (e) F V V 0c REF I (f) COMMON SWITCH ELECTROD -oc SUPPLY o.5s l- COMMON 45 (g) T| oc REF 7v (h) 7 DC REF 1 COMMON (n oc REF l REF COMMON 7 (j) .sv I I +7 0c (k) l REF COMMON *T I l (m) LOAD CURRENT FIG. 6

BIOCHEMICAL OXYGEN DEMAND SYSTEM This invention relates to a biochemical oxygen demand system and more particularly to the continuous measurement of oxygen uptake of a biological sample.

Heretofore, in a biological oxygen determination, the amount of oxygen chemically or biologically removed from a sample was determined by monitoring the on time of a constant current source supplying energy to an oxygen generator. This on time is conventionally monitored by an elapsed time meter and possibly a strip chart recorder. Such systems required continuous attention from an operator and provided usually only limited results.

The growing concern with pollution control has forced a search for more reliable and precise measurements of pollution, in particular, water pollution. Biochemical oxygen demand (BOD) has been the most widely used and is considered to produce the most meaningful measure of the level of pollution of waste water. Heretofore, the conventional BOD method has many times failed to produce satisfactory results for its lack of reproducibility, for its subjection to interferences, for the requirement of careful laboratory techniques and for the length of time required to produce a result.

In other electrolytic biochemical oxygen demand systems, a reaction chamber consisting of a one-liter stirred vessel with a monometric switch and electrolytic oxygen generator mounted in the top, provides a determination of the oxygen uptake of an inhomogeneous biological sample by chemically or biologically removing oxygen from the sample. As oxygen is chemically or biologically used, and as any CO which may be released as a metabolic end product is removed from the air space in the reaction chamber by a KOI-l solution, a slight vacuum in the air space of the reaction chamber is produced. The monometric switch is triggered and oxygen is produced electrolytically to replace the O consumed. The electrolytic oxygen generator replaces the consumed oxygen by energization from a current source. The current source having been activated by operation of the monometric switch. A determination of the oxygen consumed is made by timing the on time of the current source.

In accordance with the present invention, a biochemical oxygen demand system includes an electrolysis cell containing an electrolyte and having a monometric switch and an oxygen generator with activating electrodes. A constant current source is energized by operation of the monometric switch and connected to the electrodes of the oxygen generator for replacing oxygen consumed in a reaction chamber. Also energized by the monometric switch is a circuit for converting the ampere-second output of the constant current source, in accordance with Faradays law on electrochemistry, into electronic signals representing a measure of oxygen produced by the oxygen generator.

More specifically, a measure of the ampere-second output of the constant current source is made by generating a train of fixed width pulses spaced apart by a fixed interval of time. These fixed width pulses are applied to a pulse counter which responds thereto to produce a measure of oxygen produced by the oxygen generator.

A more complete understanding of the invention and its advantages will be apparent from the specification and claims and from the accompanying drawings illustrative of the invention.

Referring to the drawings:

FIG. 1 is a block diagram of a biochemical oxygen demand system including elements for measuring the ampere-second output of a constant current source;

FIG. 2 is a schematic of a reaction chamber and an electrolysis cell with a monometric switch and an oxygen generator;

FIG. 3 is a block diagram of the control for the oxygen generator and the system for measuring the ampere-second output of the constant current source supplying the oxygen generator with energizing current;

FIG. 4 is a schematic and block diagram of the timer and power supply of the system of FIG. 3;

FIG. 5 is a schematic of the current regulator, counter driver and switch delay circuit of FIG. 3; and

FIG. 6 is a series of waveform functions for the operation of the circuit of FIG. 5.

Referring to FIGS. 1 and 2, an incubator 10 containing a reaction chamber 12 and an alkali CO absorber 14 is maintained at a desired temperature by a temperature conditioner 16 coupled to a temperature controller 18. The temperature controller 18 responds to a temperature sensor 20 and controls the incubator 10 temperature over a range of from 15C to 50C. The reaction chamber 12 may be a standard one-liter, narrow mouth, reagent bottle as shown in FIG. 2. A sample, the pollution level of which is to be determined, is placed in the reaction vessel where a stirring magnet 24 continuously agitates the sample. In a conventional manner, the stirring magnet 24 is rotated by a magnetic stirrer (not shown in FIG. 2) located outside the reaction chamber 12. The absorber 14 may be a test tube welded to the bottom of a bushing type reducing adapter 14a.

Also associated with the reaction chamber 12, outside the incubator 10, is an electrolysis cell 26 comprised of an electrolytic oxygen generator 28 and a monometric switch 30. The electrolysis cell 26 contains an electrolyte, such as a dilute acid, for generation of oxygen by means of an electrical current applied to an oxygen electrode 32. Also forming part of the oxygen generator of the electrolysis cell 26 is a hydrogen electrode 34, the connection of which will be described. In the form shown in FIG. 2, the monometric switch 30 comprises-an electrode 36 in contact with the electrolyte.

To generate oxygen by the electrolytic oxygen generator 28, a constant current is applied to the electrode 32 from a constant current generator 38. This generator is controlled on and off from the monometric switch 30. A power supply 40 provides the energizing voltage to the generator 38.

A measure of the oxygen produced by the electrolyte generator 28 is made by measuring the ampere-second output of the constant current generator 38. This mea- Microorganisms in the sample literally eat" organics in the waste water sample and thereby consume oxygen in degrading the organics. Oxygen is thereby removed from the dissolved state in the sample. As a result, oxygen in the air space above the sample is removed. As a further reaction in the chamber 12, CO is released as a metabolic end product (produce of respiration by microorganisms} and absorbed by an alkali CO absorber (KOH solution or pellets) in the absorber 14. Since oxygen is removed from the air space and the CO produced is also removed by the alkali 'CO absorber, there a partial vacuum is created in the air space above the sample in the reaction chamber 12.

The level of electrolyte within the inner chamber 26a of the electrolysis cell 26 rises as a result of this partial vacuum and consequently the level of the electrolyte in the outer chamber 26b drops. As the level of the electrolyte in the outer chamber 26b drops, contact with the electrode 36 is broken thereby actuating the monometric switch 30. This electronically turns on the oxygen generator 28 by energizing the constant current generator 38. Oxygen is produced by the oxygen generator 28 by electrolysis of the electrolyte. This continues until the partial vacuum in the electrolysis cell 26 is satisfied by providing additional oxygen to the air space in the reaction chamber 12. The level of the electrolyte in the outer chamber 26!) again contacts the electrode 36 and the monometric switch 39 turns off the constant current generator 38. The time during which the constant current generator 38 was energized and the amount of current supplied to the oxygen generator 28 is then converted by the converter/accumulator 42 into milligrams of oxygen in accordance with Faradays law on electrochemistry.

Referring to FIG. 3, to convert the ampere-seconds output of the constant current generator into milligrams of oxygen a timing circuit is operated simultaneously with the current generator. The incubator with the reaction chamber (sample bottle) 12 and the electrolysis cell 26 are again schematically illustrated. ln addition, a magnetic stirrer 46, controlled from a speed controller &8, are shown associated with the stirring magnet 24 This is conventional apparatus provided for imparting an agitation to the sample within the reaction chamber 12.

ln the electrolysis cell 26, the hydrogen electrode 34 connects to ground at a connection 50. The oxygen electrode 32 connects to the output of a constant current source 52 and the switch electrode 36 connects to a delay generator 54. A constant current is supplied to the electrode 32 from the source 52 by operation of a constant current regulator 56 having an input in series with an adjustable resistor 58. The resistor 58 connects to the output of a current switch 60 having an input terminal tied to the output of a power supply 62 and a control terminal connected to the delay generator 54.

It will be noted in FIG. 3 that in addition to the current switch 60, the output of the power supply 62 is applied to a current switch for a second unit and a current switch for a third unit. In a typical installation of the present invention, three incubators and reaction chambers are controlled from the power supply 62. For simplicity in explanation of the invention, only one of the three systems has been illustrated, the other two being similar to that described.

In addition to supplying a DC voltage to the current switch 69, the power supply 62 also provides a reference DC voltage to the current regulator 56. The current regulator 56 also connects to positive and negative terminals of the power supply 62 to provide operating voltages thereto.

Also controlled by the delay generator 54 and connected to the power supply 62 is a time pulse generator 64. The time pulse generator 64 is another part of PK}. 3 that is common to the three systems of a typical installation. The time pulse generator 64 divides a high pulse per minute rate input signal on line 66 into a considerably slower pulse per minute rate on line 68. Line 68 is tied to the input terminal of a constant pulse width generator 70 which has an output connected to a counter driver 72. The constant pulse width generator '70 provides at its output fixed width pulses timed spaced over equal increments. These fixed width pulses are converted by the counter driver 72 into equally spaced voltage pulses applied to the input of an impulse counter 74. The impulse counter 74 registers upon a display the number of voltage pulses generated at the output of the counter driver 72. In addition to a visual display, the total number of voltage pulses at the output of the counter driver 72 may also be recorded on the automatic printout 44.

in operation of the circuit of FIG. 3, as explained, organisms consume oxygen in the sample within the reaction chamber 12. causing a partial vacuum which results in the electrolyte in the electrolysis cell 26 breaking contact with the switch electrode 36. When the electrolyte breaks contact with the switch electrode 36, the current switch 60 turns on through the delay generator 54 and an output current flows from the current source 52 to the oxygen electrode 32 thereby generating oxygen within the electrolysis cell 26.

The amount of oxygen generated in the cell 26 is determined by using Faradays law of electrochemistry to convert the ampere-seconds output of the current source 52 into milligrams of oxygen. This is accomplished by activating the time pulse generator 64 through the delay generator 54 from the electrode switch 36 at the same time the current switch 60 is turned on.

Assume that the input to the time pulse generator 64 on the line 66 is 3600 pulses per minute, then the output of the time pulse generator is 1/600 of this or ID pulses per minute. This pulse train commences at the time the electrolyte breaks contact with the electrode switch 36; it is applied to the input of the constant pulse width generator 70. Each pulse input to the constant pulse width generator 70 produces a fixed width output pulse to the counter driver 72. in one embodiment of the invention, the generator 70 produces a 350 millisecond pulse every six seconds to the input of the counter driver 72. The counter driver 72 is essentially a power amplifier thatprovides a voltage pulse for each 350 millisecond pulse applied to the input thereof. Each voltage pulse output of the counter driver 72 advances the count of the impulse counter 74 one count.

In accordance with Faradays law on electrochernistry, if the current source 52 is supplying 200 milliamps of current through the electrolyte solution of the electrolysis cell 26, then 0.1 milligrams of oxygen will be generated each six seconds. Thus, if the counter driver 72 produces one voltage spike for each constant width pulse output of the generator 70, then the impulse counter 74 advances one count each 6 seconds. Since the time pulse generator 64 and the current switch 60 are actuated simultaneously, the total count registered in the impulse counter 74 is a running tabulation of the milligrams of oxygen generated in the electrolysis cell 26.

As more oxygen is generated in the electrolysis cell 26 than consumed by the organisms within the reaction chamber 12, the electrolyte again contacts the electrode switch 36 and the current switch 60 is immediately turned off along with the time pulse generator 64. The total count registered in the impulse counter 74 represents the amount of oxygen produced by the electrolysis cell 26 during operation of the current source 52.

The time pulse generator 64 operates such that the time interval between a six second pulse is divided into 600 parts. Assume that the switch electrode 36 makes contact with the electrolyte three seconds after a count is registered in the impulse counter 74. In this situation, 300 bits of a possible 600 are stored in the time pulse generator 64 by the normal operation thereof. Thus, if an additional energizing signal is received from the electrolysis cell 26, only 300 additional bits are required for the first output pulse on the line 68. This allows a small switching error to occur between counts.

To prevent such errors from occurring, the delay generator 54 is actuated upon each breaking of contact of the electrolyte with the electrode switch 36. This sets the delay generator 54 and a timer begins to hold the current off to the electrolysis cell 26 for a fixed period of time. In one working model of the invention, a one minute time delay was employed. Thus, if the current source 52 is turned off by the electrolyte contacting the switch 36, it cannot be restarted for a period of one minute regardless of whether the electrolyte again breaks contact with the electrode switch 36. If after the one minute delay, the electrode switch 36 is still not in contact with the electrolyte, then the current switch 60 and the time pulse generator 64 are actuated and operate in the manner previously described.

Referring to FIG. 4, there is shown a schematic of the power supply 62 and the time pulse generator 64. The power supply 62 includes an input transformer 73 supplying an AC voltage to a rectifying bridge consisting of diodes 75-79. A voltage at the positive terminal of the rectifying bridge is filtered by a capacitor 80 to generate a DC voltage for the current switch 60 and the current switches of additional units in the system. The negative voltage at the junction of diodes 75 and 76 is filtered by a capacitor 82 and provides a DC reference voltage for the time pulse generator 64 and the current regulator 56 and for similar components of additional units in the system. The DC reference voltage is provided at the junction of the Zener diode 84 and the filter capacitor 86. A bias current for the Zener diode 84 is developed through a resistor 88. This negative DC reference voltage is applied to the constant current regulator 56. A positive DC regulated voltage is supplied to the time pulse generator 64 from the cathode electrode of Zener diode 90 biased by a resistor 92.

The positive voltage at the cathode electrode of the Zener diode 90 is applied to a NAND gate register 96, divide-by-six registers 94 and 98 and a divide-by-ten register 100 of the generator 64. This voltage is also supplied to registers 102-105 for additional units in the system. To understand the operation of the invention, only the registers 98 and 100 will be considered.

One terminal of the secondary winding of the transformer 72 provides the Hz frequency to the time pulse generator 64 over the line 66. This 60 Hz fre quency is connected to a divide-by-six shift register 94 through a voltage divider including resistors and 97. The register 94 divides the 60 Hz frequency into a 600 cycle per minute signal applied to the NAND gate register 96. Capacitor 94a filters high frequency noise from the 60 Hz power input to the register 94.

The gate register 96 is operated open and allows the 600 counts per minute to be applied directly to counter 98. Upon receipt of a second input on line 106, the part of NAND gate register 96 associated with the first unit, the gate closes to stop transfer of the 600 cycle per minute voltage from the register 94 to the divide-by-six register 98. Subsequently, the cycle per minute output of the register 98 is applied to the divide-by-ten register 100. Through operation of the register 100, a 10 pulse per minute output signal is produced on the line 68 to the constant pulse width generator 70.

Referring to FIG. 5, there is shown a schematic of the constant pulse width generator 70 and the counter driver 72 in addition to the current switch 60, the constant current regulator 56 and the current source 52. In practice, these units are constructed on a single printed circuit board. Thus, they are described in the same figure.

Considering first the current switch, current regulator and current source, an operational amplifier 108 drives a transistor 110 through the base electrode thereof. Additional passive circuitry for the amplifier 108 includes bias resistors 112 and 114 having an interconnection to the cathode electrode of the Zener diode 90 through a resistor 116. The transistor 110 is part of the current source 52 and comprises part of the negative feedback path for the operational amplifier 108. Also included, but outside the feedback loop, is the current adjust variable resistor 58. A voltage divider network of resistors and 122 provides a resistance for proper amplifier gain.

The operational amplifier 108 is turned on by operation of a transistor 124 having a base electrode connected to the reference voltage at the anode of the Zener diode 84 through a resistor 126. Conduction of the transistor 124 is controlled by the delay generator 54 and in particular, a transistor 128. Transistor 124 controls the operational amplifier 108 through a collecter emitter circuit including resistor connected to the base electrode of a transistor 132.

In operation, the operational amplifier 108 provides a constant base drive current to the transistor 110 independent of the current demand at the collecter electrode thereof which connects to the oxygen electrode 32 of the electrolysis cell 26. By means of the resistor 58, a variable constant current source is provided with the current remaining constant for a load resistance variable over a considerable range.

As previously mentioned, control of the operational amplifier 108 is through a transistor 124 in turn controlled by a transistor 128 of the delay generator 54. The switch electrode 36 of the electrolysis cell 26 connects to the base electrode of a transistor 134 through a base drive resistor 136. Also in the base-emitter path of the transistor 134 is a filter capacitor 138 and an emitter resistor 140.

Conduction of the transistor 134 provides a gate voltage to a silicon controlled rectifier 142 in the emitter electrode circuit of the transistor I28. Transistor 128 turns on through a base current provided by a resistor 144 and a voltage is developed across a resistor 146. The voltage developed across the resistor l ldcauses a charge build-up on a capacitor 148 through a resistor 25% to the firing point of a unijunction transistor I52. When the transistor 152 fires, a silicon controlled rectifier 15 i is caused to conduct thereby turning off the transistor 128 and resetting the silicon controlled rectifier 1 12.

This provides a time delay during which the voltage drop across transistor 123, silicon controlled rectifier I42 and resistor i to reverse biases the transistor 124 which is normally forward biased through the resistor 126. After the time interval, transistor 12% conducts thereby turning on transistor 132 and constant current is provided to the oxygen electrode 32. However, when the silicon control rectifier 142 is nonconducting and the transistors 12d and 132 are off, no current flows to the oxygen generator. That is, as long as the electrolyte is in contact with the electrode switch 36 no current flows and no oxygen is generated. Once the electrolyte level falls below the position of the switch electrode 36, then current flows to the oxygen electrode 32 after the time delay provided by the unijunction transistor 1S2 circuit. As mentioned, this time delay alleviates causing errors during current switching.

During the time delay provided by the delay generator 54, current is provided to a transistor 15s through a resistor 15%. Transistor l56 connects the NAND gate registers 96 of the pulse generator 64. Thus, the time pulse generator 64 is simultaneously controlled with the constant current source 52. The constant current source is controlled through the transistor I24 and the time pulse generator 64 is controlled through the transistor 1 56.

The 10 pulses per minute from the divide-by-ten register MM are applied to a timed input terminal MA}. A capacitor M52 and a resistor 16% differentiates the rect angular input wave at the terminal 151) thereby provid ing voltage pulses to the gate electrode of a silicon controlled rectifier loo. Conduction through the rectifier 166 turns on a transistor I68 through a base drive resistor 317i Conduction of the transistor E68 actuates a photo relay i'72 to drive a Triac 1.74. The Triac 174 has one terminal tied to an alternating current source and a second terminal to the input of the impulse counter 74L.

Also resulting from conduction through the rectifier I166 is the forward biasing of a transistor 176 through a base resistor ll7$ and a resistor R80. With transistor I76 turned on, a voltage is developed across the resistor llStll and a charge begins to build-up across a capacitor ll82 through a resistor E841 until the firing point of an unijunction transistor M56 is reached. Transistor 186 fires and sufficient voltage is developed across a resistor 183 to turn on a silicon controlled rectifier 190 having an anode electrode connected to the resistor I70.

Turning on the rectifier W0 clamps the base elec' trode of the transistor N58 to essentially the DC reference voltage and this transistor turns off. Resistor 17h is sized to prevent the rectifier we from latching on and thus, after the unijunction transistor 186 resets, the rectifier we turns off.

Turning off the transistor ll68 also resets the rectifier 166 thus reestablishing the circuit for controlling the relay l72. The counter 74 advances one count when the transistor 168 turns off. The capacitor I82 and the resistor I84 establishes the pulse width of the voltage driving the counter 74.

Referring to FIG. 6, there is shown a series of waveform functions generated in the circuit of FIG. 5. The timer input waveform is illustrated at FIG. 6a and consists of a series of pulses spaced each 6 seconds. These pulses are differentiated by the capacitor I62 and the resistor 164 to produce positive and negative going pulses as illustrated in FIG. 6b. This waveform appears at the junction of the capacitor 162 and the resistor 164. Timing pulses generated by the capacitor 182 and the resistor 184 are shown in FIG. 6d and appear at the junction of the resistor 184 and the capacitor 182. By firing the unijunction transistor 186 with the pulses as illustrated in FIG. 6d, the rectifier 190 conducts to pro duce the pulse train as illustrated in FIG. 6e. This waveform appears in the circuit of FIG. 5 at the anode electrode of the rectifier 190. This series of pulses controls conduction in the transistor 168 thereby generating pulses of constant width at the collecter electrode of transistor 168 as shown in FIG. 60. These constant width pulses, 350 milliseconds in the previous example, appear at the output of the constant pulse switch gener ator 70. In effect then the transistor 168 comprises the constant pulse width generator output circuit. These constant width pulses control the counter driver 72 which in FIG. 5 includes the photo relay 172 and the Triac E74.

Waveforms of FIG. 6f-6j are a function of the delay generator 54. The trigger pulse produced by the electrode switch 36 is shown in FIG. fto turn on the transistor 1341. Turning on the transistor 134 triggers the rectifier I42 by the function shown at FIG. 6g. Conduction of the rectifier 142, as explained, provides a voltage drop across the resistor 146 and a timing function is generated by the capacitor 148 and the re sistor I50. This function is illustrated at FIG. oh and appears in the circuit of FIG. 5 at the junction of resistor i150 and capacitor 148. Firing of the unijunction transistor 152 turns on the rectifier 154 and a voltage spike, as illustrated at FIG. 6:, is generated at the anode electrode thereof. By operation of the transistor 128, as explained previously, a function as shown in FIG. 6j is generated at the base electrode of the transistor 124. This controls conduction of the transistor 124 to produce the function of FIG. 6k at the base electrode of transistor 132. Transistor 132, as explained, controls the operational amplifier E08 which in turn controls the transistor 116 to produce the waveform of FIG. 6m at the emitter electrode of transistor 110.

The waveform of FIG. 6m shows the constant current supplied to the oxygen electrode 32 of the electrolysis cell 26. It is this ampere-second output from the transistor H0 that is converted into milligrams of oxygen in accordance with Faradays law on electrochernistry. The measure of milligrams of oxygen produced by the electrolysis cell 26 appears as an impulse count in the counter 74 by operation of the time pulse generator 64, the constant pulse width generator and the counter driver 72.

While only one embodiment of the invention, together with modifications thereof, has been described in detail herein and shown in the accompanying drawings, it will be evident that various further modifications are possible without departing from the scope of the invention.

What is claimed is:

1. Oxygen measurement apparatus for a biochemical oxygen demand system including an electrolysis cell containing an electrolyte and having an oxygen genera tor with activating electrodes and a monometer controlled switch energizing a constant current source connected to the electrodes of the oxygen generator for supplying an ampere-seconds output to generate oxygen in the electrolysis cell, the improvement comprising:

a time pulse generator energized by the monometer controlled switch for producing timing pulses at intervals related to the ampere-second output of the constant current source such that each pulse represents a calculated milligrams of oxygen generated by the oxygen generator,

a fixed width pulse generator connected to said time pulse generator for converting the output pulses thereof into a series of fixed width driving pulses, and

counter means responsive to each driving pulse from said fixed width pulse generator for totaling the milligrams of oxygen generated by the oxygen generator during the energization of the constant current source 2. Oxygen measurement apparatus for a biochemical oxygen demand system as set forth in claim 1 wherein said time pulse generator produces one pulse each 6 seconds and each pulse represents 0.1 milligrams of oxygen generated by said oxygen generator.

3. Oxygen measurement apparatus for a biochemical oxygen demand system as set forth in claim 1 including delay means connected between the monometer controlled switch and said constant current source and said time pulse generator to delay the energization of the former and the actuation of the latter.

4. Oxygen measurement apparatus for a biochemical oxygen demand system as set forth in claim 1 including a counter driver interconnected between said fixed width pulse generator and said pulse counter to convert the fixed width pulse output to the former into driving pulses for the latter.

5. Oxygen measurement apparatus for a biochemical oxygen demand system as set forth in claim 4 wherein said driver means includes a silicon controlled rectifier having a gate electrode connected to the output of said pulse generator means and an output transistor connected to a unijunction transistor circuit and the anode electrode circuit of said silicon controlled rectifier.

6. Oxygen measurement apparatus for a biochemical oxygen demand system as set forth in claim 5 including a photo relay in the output circuit and said transistor for isolating the counter means from noise nad transient signals. 

1. Oxygen measurement apparatus for a biochemical oxygen demand system including an electrolysis cell containing an electrolyte and having an oxygen generator with activating electrodes and a monometer controlled switch energizing a constant current source connected to the electrodes of the oxygen generator for supplying an ampere-seconds output to generate oxygen in the electrolysis cell, the improvement comprising: a time pulse generator energized by the monometer controlled switch for producing timing pulses at intervals related to the ampere-second output of the constant current source such that each pulse represents a calculated milligrams of oxygen generated by the oxygen generator, a fixed width pulse generator connected to said time pulse generator for converting the output pulses thereof into a series of fixed width driving pulses, and counter means responsive to each driving pulse from said fixed width pulse generator for totaling the milligrams of oxygen generated by the oxygen generator during the energization of the constant current source.
 2. Oxygen measurement apparatus for a biochemical oxygen demand system as set forth in claim 1 wherein said time pulse generator produces one pulse each 6 seconds and each pulse represents 0.1 milligrams of oxygen generated by said oxygen generator.
 3. Oxygen measurement apparatus for a biochemical oxygen demand system as set forth in claim 1 including delay means connected between the monometer controlled switch and said constant current source and said time pulse generator to delay the energization of the former and the actuation of the latter.
 4. Oxygen measurement apparatus for a biochemical oxygen demand system as set forth in claim 1 including a counter driver interconnected between said fixed width pulse generator and said pulse counter to convert the fixed width pulse output to the former into driving pulses for the lAtter.
 5. Oxygen measurement apparatus for a biochemical oxygen demand system as set forth in claim 4 wherein said driver means includes a silicon controlled rectifier having a gate electrode connected to the output of said pulse generator means and an output transistor connected to a unijunction transistor circuit and the anode electrode circuit of said silicon controlled rectifier.
 6. Oxygen measurement apparatus for a biochemical oxygen demand system as set forth in claim 5 including a photo relay in the output circuit and said transistor for isolating the counter means from noise nad transient signals. 